Cornball chemistry

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Monthly Archives: October 2013

Fluorescent ink is easy to extract from highlighter pens and makes a great halloween chemistry display when illuminated under uv light.
Last time I asked if you could calculate the enthalpy of reaction for the reaction between hydrogen and fluorine using the bond energies supplied. Here is how you do it:

The bond energy approach to calculating an enthalpy change for a reaction

Hydrogen and fluorine react spontaneously, but a mixture of hydrogen and oxygen needs a spark in order to make it explode. The reason for this is that the spark provides the activation energy needed by the molecules of hydrogen and oxygen immediately surrounding it to react. Since the reaction between these molecules is exothermic, they in turn provide the activation energy to cause further molecules of hydrogen and oxygen in close proximity to also react. In an instant, these processes extend throughout the mixture until all of the hydrogen and oxygen molecules have reacted.

Finally, when molecules ammonia and hydrogen chloride gases are brought together they react spontaneously to form solid ammonium chloride. In a diffusion tube experiment this is seen as a cloud of white smoke at the point where the two gases meet. Ammonium chloride is an ionic solid and the formation of the ionic bonds is an exothermic process as illustrated by the images below.

Ammonia and hydrogen chloride diffusion experiment at the start

Ammonium chloride produced as a white cloud

Temperature probe moved into the cloud of ammonium chloride being formed

Maximum temperature increase – an exothermic reaction

Smaller animated gif which should show motion within the blog

Large animated gif of the experiment – download to view

Can you write a balanced symbol equation for the reaction between ammonia and hydrogen chloride?
And why do fluorescent inks glow?